The present invention relates to a method for the preparation of a protein in a biologically active or native form.
Recombinant DNA technology provides potentially extremely valuable means of synthesizing amounts of desirable eukaryotic (usually mammalian) proteins such as hormones, interferons, and enzymes. Although it has proved to be relatively easy to manipulate organisms such as bacteria to produce the desired protein, the host organism does not normally secrete the over-produced protein product into the culture medium. Thus lysis of the organisms (for example bacteria), followed by isolation of the desired protein is usually necessary.
A protein exists as a chain of amino acids linked by peptide bonds. In the normal biologically active form of such a protein or its native form as it is commonly referred to, the chain is folded into a thermodynamically preferred three dimensional structure, the conformation of which may be maintained by steric interaction intermolecular and intramolecular forces such as hydrogen bonding, hydrophobic interactions and charge interactions. In the prior art, the usual aggregation and insolubility under folding conditions of fully, or partially, unfolded proteins requires that folding be carried out in the presence of denaturants, reducing agents and in very dilute solutions, consequently, in large volumes. The handling of such dilute solutions and large volumes together with toxic reducing agents such as B-mercaptoethanol adds significantly to the cost when such processes are applied industrially.
In U.S. Pat. No. 4,797,474, the disclosure of which is herein incorporated by reference, applicants have described a highly economical method for the recovery of proteins in a soluble form from an insoluble protein source utilizing a cationic surfactant. Whilst this process allows for the efficient recovery of proteins in a soluble form, the proteins may not exhibit their normal biological activity. The proteins so recovered may not be in their native form.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties related to the prior art.